diff usage reminder

• by convention (Wiki), the first file argument should be the original, and the second should be the new version
• first file argument is the one listed above the --- fold, the second below it
• in this context, an addition/insertion is represented with a < and a removal/deletion with >
  • < above the fold = "has come in" (has replaced what's below the fold)
  • > below the fold = "has gone out" (has been replaced by what's below the fold)

A diff call will not necessarily give the same numbers of lines above and below the fold with the file arguments passed in a different order!

The output of diff is plaintext